Various coating materials have been used on optical fibers, for maintaining the strength of the fibers and protecting them from microbending, which induces optical loss. These materials include those which are cured by UV-ray or heat after being coated on the fibers, and those which are cured by evaporation of the solvent after coating with a material containing a solvent, as the main materials. Recently, however, for improving the workability in the coating step or physical properties of the coating material, as pointed out in Japanese unexamined patent publication (Kokai) No. 58-100102, hot melt materials have been used.
Also, there has been a demand for hot melt adhesives, in general, having an excellent adhesiveness at lower temperatures. The above mentioned Japanese unexamined patent publication (Kokai) No. 58-100102, proposed a hot melt composition which can be advantageously applied for optical fiber, but it did not have a sufficiently small modulus at low temperatures, which is an important physical property of the coating material for an optical fiber for the prevention of optical loss by microbending, and a coating material superior in various other points has been sought.